1. Field of the Invention
The present invention relates to a radio frequency module. The present invention relates particularly to a radio frequency module incorporating a monolithic microwave integrated circuit (hereinafter abbreviated to an MMIC) fabricated by using a field effect transistor capable of achieving a high S/N ratio. More particularly, the present invention relates to a field effect transistor that can achieve a high S/N ratio. Still more particularly, the present invention relates to a module for moving target detection.
2. Related Arts
For a radio frequency module, especially a module required to provide a high output, the following techniques are employed. For high output, there is known a technique in which a high electron mobility transistor, commonly referred to as a HEMT, which has a channel layer of high indium content is used in an MMIC including an amplifier (hereinafter abbreviated to an amplifier MMIC). This technique is intended to improve device current drivability and increase output of the amplifier MMIC by using a channel layer of high indium content, for example a layer of indium, gallium, and arsenic having a high mobility and a high saturation rate. The technique is described in the IEEE MICROWAVE AND GUIDED WAVE LETTERS Vol.4 No.8, pp.277-278, for example.
In addition, for high output of an amplifier MMIC, there is known a technique that uses a HEMT whose channel layer comprises a layer of indium, gallium, and arsenic and a layer of indium and phosphorus. This channel structure is referred to as a composite channel. A conventional technique that uses a HEMT having a composite channel in an amplifier MMIC is described in the IEEE Transactions on Electron Devices Vol.42 No.8, p.1413, for example.
It is accordingly an object of the present invention to provide a radio frequency module incorporating an MMIC that has a high S/N ratio while ensuring a high output. More technically, the present invention is intended to achieve high S/N ratio of a field effect transistor that is a main active device forming an amplifier, an oscillator, or a mixer of the MMIC. In addition, the present invention is intended to enable the field effect transistor to have a high S/N ratio while ensuring a high output. Problems in achieving the above are factors that cause degradation in characteristics of a monolithic microwave integrated circuit having an oscillator formed with the field effect transistor (hereinafter abbreviated to an oscillator MMIC), an amplifier MMIC, and the like. Problems in achieving the above are factors that cause degradation in characteristics of a transmitter or a receiver having such an oscillator MMIC or an amplifier MMIC. The oscillator MMIC particularly has a problem of degradation in noise characteristics, while the amplifier MMIC particularly has a problem of difficulty in achieving high output at its amplifying stage, especially at its final stage. The amplifier MMIC also invites degradation in noise characteristics.
Accordingly, it is another object of the present invention to provide a radio frequency module that includes an oscillator or an amplifier having excellent S/N characteristics.
Various forms of field effect transistors used in conventional radio frequency modules, typified by a HEMT, each have problems that make it difficult to fully meet objects of the present invention. In addition to a HEMT with an ordinary structure, a HEMT with a composite channel has been proposed. The HEMT with a composite channel serves an object of the present invention to achieve high current drivability and high breakdown voltage.
A field effect transistor according to the present invention is intended to prevent breakdown due to physical characteristics of its channel materials or to avoid a problem of increase in noise caused by the composite channel. In other words, the present invention is intended to avoid problems of the composite channel and achieve both high current drivability and high breakdown voltage.
Radio frequency modules according to the present invention have the following configurations.
According to a typical aspect of the present invention, there is provided a radio frequency module comprising monolithic microwave integrated circuits on a single substrate which include at least an oscillator, an amplifier, and a receiver, at least one of the oscillator, the amplifier, and the receiver including a field effect transistor having a channel region with a junction of two or more different kinds of materials.
According to another aspect of the present invention, there is provided a radio frequency module comprising an amplifier MMIC portion including at least a field effect transistor, the field effect transistor having a channel region with a junction of two or more different kinds of materials, and height of a potential barrier of a junction interface between the different kinds of materials in the channel region being less than 0.22 eV.
According to a further aspect of the present invention, there is provided a radio frequency module comprising an oscillator MMIC portion; an amplifier MMIC portion for amplifying an output signal of the oscillator MMIC portion; a receiver MMIC portion for amplifying a received signal; and a terminal for extracting an intermediate frequency signal by mixing an output signal from the receiver MMIC portion with the output signal from the oscillator MMIC portion; the oscillator MMIC portion, the amplifier MMIC portion, the receiver MMIC portion, and the terminal being mounted on a single semiconductor substrate, and at least one of the oscillator MMIC portion, the amplifier MMIC portion, and the receiver MMIC portion including a field effect transistor having a channel region with a junction of two or more different kinds of materials.
According to a further aspect of the present invention, there is provided a radio frequency module comprising an amplifier MMIC portion including at least a field effect transistor; and an oscillator MMIC portion including at least a field effect transistor, the field effect transistors each having a channel region with a junction of two or more different kinds of materials, and height of a potential barrier of a junction interface between the different kinds of materials in the channel region, experienced by conductor carriers, being less than 0.22 eV.
According to the present invention, it is particularly important that the height of a potential barrier of an interface between the different kinds of materials be less than 0.22 eV. Reasons for this will be described later.
According to a further aspect of the present invention, there is provided a module for moving target detection comprising monolithic microwave integrated circuits on a single substrate which include at least an oscillator, an amplifier, and a receiver, at least one of the oscillator, the amplifier, and the receiver including a field effect transistor having a channel region with a junction of two or more different kinds of materials. According to a further aspect of the present invention, there is provided a module for moving target detection, wherein height of a potential barrier of a junction interface between the different kinds of materials in the channel region is less than 0.22 eV.
The field effect transistor according to the present invention can be configured as various field effect transistors such as a HEMT, a MESFET (Metal Semiconductor Field Effect Transistor) and a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The HEMT is especially useful for radio frequency applications in the present invention.
In general, such a field effect transistor is formed of compound semiconductor materials. A typical example of the compound semiconductor materials is III-V compound semiconductor materials, and among others, InP compound semiconductor materials are often used.
The HEMT is a field effect transistor comprising a first semiconductor layer containing an impurity; and a second semiconductor layer having a smaller band gap than that of the first semiconductor layer, the first semiconductor layer and the second semiconductor layer being joined together to form a heterostructure, the second semiconductor layer containing substantially no impurity, and the second semiconductor layer or an interface of the heterostructure functioning as a channel region. A gate electrode is disposed on the side of the first semiconductor layer containing an impurity. A channel region formed by a plurality of semiconductor layers is referred to as a composite channel. As described above, this composite channel is useful in achieving high output. The band gap of a semiconductor layer of the composite channel on a side farther from a gate electrode is generally selected to be larger than that of a semiconductor layer on the gate electrode side.
The gate electrode side is generally disposed on a side opposite from a crystal substrate with the channel region intermediate between the gate electrode side and the crystal substrate; conversely, of course, the gate electrode side may be disposed on the crystal substrate side. Thus, the HEMT in the present specification may be formed by making various common modifications thereto in accordance with the technical concept of the present invention.